高一数学:求值域

y=x^2-x/(x^2-x+1)
=(x^2-x+1-1)/(x^2-x+1)
=1-1/(x^2-x+1)
=1-1/((x-1/2)^1+3/4)
分母大于等于3/4
值域y(-无穷,-1/3]

y=2x^2-2x+3/(x^2-x+1)
（2x^2-2x+2+1）/(x^2-x+1)
=2+1/(x^2-x+1)
=2+1/((x-1/2)^2+3/4)
分母大于等于3/4
值域y (-无穷，10/3

y=x^2-x/(x^2-x+1)
=1-1/(x^2-x+1)
=1-1/[(x-1/2)^2+3/4]
>1-1/(3/4)
=1-4/3
=-1/3

值域为【-1/3，正无穷】

y=2x^2-2x+3/(x^2-x+1)
=2+1/(x^2-x+1)
=2+1/[(x-1/2)^2+3/4]

<（小于等于）2+1/(3/4)

=10/3
=3又1/3

值域为【负无穷，3又1/3】